The state of disuse.
A very fancy way of saying “unused.”
Etymology: early 17th century (in the sense ‘cessation’): from French, from Latin desuetudo, from desuet- ‘made unaccustomed’, from the verb desuescere, from de- (expressing reversal) + suescere ‘be accustomed’.
A word I sort of like, because it has mnemonic de-“use”tude scrambled into the middle, and that makes the word, which itself is (fittingly!) a relatively unused word, sort of look like it has fallen into disrepair; as if at some point its letters got jumbled from their proper order after years of neglect.